The purpose of the rollover detection system is to activate protection devices such as seat belts pretensioners, pop-up rollover bars or air bags, protecting occupants of a vehicle during rollover accidents.
Rollover occurrences may be categorized by various types. For example a fall-over or flip-over occurs when one wheel of the vehicle goes respectively excessively down or excessively up when the vehicle travels so that it rolls over. Most of the current algorithms for detecting these types of rollover use an angular rate sensor (ARS) to measure the vehicle roll rate and to calculate the vehicle roll angle (inclination) with respect to the horizontal plane by integrating the roll rate signal. On the basis of the roll rate and roll angle, these algorithms compare the kinetic energy of the vehicle to known rollover and non-rollover events (or to positional energy) in order to asses the rollover probability. Examples of such solutions are disclosed in U.S. Pat. No. 6,584,388 or 6,535,800. In case of a fall-over or flip-over it is sufficient if the vehicle protection devices are activated at the beginning of the rolling over process.
Another rollover type is a trip-over such as curb-trip or soil-trip event that occurs some time after the vehicle sideslips. In this case vehicle passengers are subjected to dangerous high lateral acceleration before the vehicle starts rolling, so that the vehicle protection devices should be activated much earlier before the actual rollover, in order to avoid injuring passengers by for example hitting against vehicle's pillars or window glass. However, the methods employing only the ARS sensor signal activate safety restraints late, during rollover events where the high lateral acceleration is present. The reason is that during trip-over, lateral acceleration creates torque acting on the car and this kinetic energy transforms into rotational energy, which is usually not taken into account by known methods. Although some rollover algorithms use the lateral acceleration signal in the sensing path, in most cases it is employed only in safing logics or to increase the estimated roll angle accuracy. To shorten the activation of protection devices, it has been proposed in a rollover judging device disclosed in patent application US 2005/0159864 to employ a differential value of an acceleration of the vehicle in a lateral direction and to judge the possibility of a trip-type rollover of the vehicle on the basis of at least one of a roll rate and a roll angle achieved by integrating the roll rate, and at least the acceleration differential value.
However there is still a need to provide a vehicle rollover detection means that would guarantee shorter deployment times for safety restraints during rollover accident and in particular during a soil trip rollover type.